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Venomous and Sublime: The Viper Tells Its Tale

Not long ago in Zion National Park in southern Utah, a couple of hikers -- O.K., one of them was this writer -- came upon a big and handsome Western rattlesnake off to the side of the trail. The snake was coiled on a rocky outcropping just below eye level, sunning itself, as ectotherms love to do. A dappled velvet cable at home on the checkerboard stage of the desert.

Soon, a throng of other hikers had gathered round to gawk, leaning in to take pictures and then squealing excitedly as the snake snapped its head toward a camera flash with a withering glower. When a park ranger arrived to see what the fuss was about and said yes, it was a real rattlesnake with genuine venom in its fangs, a teenage girl in the throng breathed out a sentiment surely shared by the group: ''That is so cool! I've never seen one of these things outside a zoo before.''

Is there anything cooler than a snake or more evocative of such a rich sinusoidal range of sensations? Snakes are beckoning. Snakes are terrifying. Snakes are elegant, their skins like poured geometry.

Snakes are preposterous. Just watch one galumph its jaws around a stunned hare or a chicken egg or even another snake.

Around the world, people dream of snakes more than of any other animal. As scientists learn more about the biology, evolution and behavior of these earthiest and most Freudianized of creatures, snakes just keep getting cooler, a fitting fate for a coldblooded reptile.

Lately, biologists have been particularly mesmerized by the large, ancient and wildly diverse group of snakes called the vipers, a family that includes rattlesnakes, coral snakes and black mambas and more than 200 other species dispersed across every continent, save Australia.

Some, like the rattlesnake, are pit vipers, with specialized concave pits between the snout and mouth that pick up heat signals from prey and foe alike. Others are pit-free.

Many New World vipers have elaborate rattles, a posterior shingling of fingernail-like plates that can shake a warning at 50 beats a second.

All vipers, however, are equipped with their signature erectile fangs, a cleverly designed set of daggerlike venom delivery devices that lie flat against the snake's upper palate when the mouth is closed, but that pop out to unexpectedly nightmarish dimensions when the snake is poised to strike.

Whereas most snakes lay eggs, a great majority of vipers give birth to live young, a fact reflected in the family name, taken from the Latin words vivo, meaning live, and partus, birth.

The vigor of the viper calling is shown in ''Biology of the Vipers,'' a generously illustrated volume being published by Eagle Mountain Publishing. In it, several dozen herpetologists offer an array of surprising, amusing and cautionary findings about their snakes.

They describe hawkish vipers and stalker vipers, males that devote the bulk of their mating energy to fighting other males and males that opt instead to pester a female, tailing behind her, interfering with her hunting and otherwise preventing her from choosing another forked tongue in the road.

They talk, as well, of the sweeter side of serpenthood, of vipers that seem to recognize their kin and seek out their siblings preferentially when it is time to den down and curl up for the winter; and of mothers that are anything but coldhearted.

Dr. Harry W. Greene of Cornell and his co-workers describe cases of parental behavior among black-tailed and pygmy rattlesnakes that defied all their presumptions.

''We'd expected that after giving birth the mothers would crawl one way and the babies another,'' Dr. Greene said.''But instead, we'd find a mother basking with her young day after day or guarding the entrance to a burrow while the babies were inside.'' Once, he said, he saw a little viper start to emerge from its hole, apparently against its mother's better judgment. ''She put her head on him and nudged him back inside.''

The researchers propose that parental behavior has evolved among some vipers, together with delayed skin shedding. While most baby snakes shed their skins as soon as they are born, viper newborns, which are comparatively larger, do not discard their birthday suits until they are about 10 days old. While they are shedding that skin, their eyes are beclouded, they are susceptible to water loss, and they are extremely vulnerable. Hence the need for a mother's watchful care.

Though snakes have long been viewed as little more than preprogrammed pinheads -- ''pretty low on the totem pole in intelligence,'' as one herpetologist put it -- Dr. Randall S. Reiserer of Vanderbilt University in Nashville tenders evidence that vipers can in fact learn from experience and fine tune their hunting strategies to suit new circumstances.

He took 10 young massasauga vipers into his laboratory, some from swampy regions of the Eastern United States and others from the Arizona deserts. As a rule, Eastern massasaugas lure fast-moving frogs by giving undulatory wiggles of their tail, which resembles a worm. But when they see a slower-moving lizard, they do not risk a tail nip and instead pursue on their bellies.

Western massasaugas, by contrast, are faced with fast-darting desert lizards. So they use their tails as lures, while they ignore the few frogs in the area as too toxic.

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Dr. Reiserer showed that despite their different origins Western vipers could learn to hunt like Easterners, with tail wagging for frogs and pouncing on slow lizards, and Easterners could be trained to wag for lizards and eschew frogs.

''Snakes turn out to be very complicated creatures,'' he said. ''But they have few ways to express what they know. It's easy to underestimate a tube.''

''We're becoming more like primatologists in our thinking,'' said Dr. Gordon W. Schuett of Georgia State University and Zoo Atlanta, an editor of the new book. ''We're tracking individual snakes for long periods of time to see who they hang out with and whom they might even form pair bonds with.''

Beyond behavioral findings, herpetologists also continue to be impressed by viper physiology. Dr. Akira Mori of Kyoto University and his colleagues describe the hypothermal prowess of the hime-habu, a short stout-bodied nocturnal viper that does not recoil from the cold, found on Okinawa and other islands of the Ryukyu Archipelago.

As ectotherms, snakes depend on heat from the outside to warm their bodies and allow them to move, hunt and digest the fruit of that hunt. When the temperature falls below 50, most snakes are virtually immobilized. If they have food in their bellies, they have to regurgitate it, for they can no longer digest the prey and could end up dying from the effects of rotting flesh within. Snakes that live in cold climates hibernate on empty bellies through the winter.

The hime-habu viper, however, has evolved the ability to continue feeding in spurts from December through March, even when temperatures dip into the 40's. With that capacity, unrivaled among vipers and, possibly, among all snakes, the hime-habu can take advantage of a rich source of food unexploited by competing reptiles, two species of frogs that gather near mountain streams by the hundreds for a few frenzied days of breeding.

Dr. Mori and his co-workers found that the vipers somehow knew exactly when the frog fest was scheduled and that they appeared at the right spot at the right time and then quickly gulped down five or more frogs in an evening. They spend the next couple of weeks digesting the meal, despite the measurable chilliness of their bodies.

Somehow, perhaps because their venom is especially suited to help process frog meat or because they have evolved mechanisms yet to be determined that keep their metabolic fires stoked in the absence of external heat, the snakes do just fine when they dine.

''You won't find a group of snakes that's more ecologically diverse and evolutionarily fascinating than the vipers,'' Dr. Jonathan A. Campbell of the University of Texas at Arlington said. ''The northernmost snake in the world is a viper, which is found in the Arctic Circle, in Scandinavia. The southernmost snake is also a viper, living in Patagonia. The two snake species that live at the highest elevation in the world are both vipers, one in the Himalayas, another in the mountains of Mexico. And their beauty? Even those who don't like snakes have to admit their beauty.''

That serpentine beauty, though, may be only skin deep.

Dr. Harvey B. Lillywhite and his co-workers at the University of Florida in Gainesville describe their discovery in a number of viper species of what Dr. Lillywhite has termed ''adaptive constipation.'' They report that, among some of the ground-dwelling vipers, defecation is a shockingly rare event. Gaboon vipers of Africa, for example, will go for a year or more without disposing waste, even as they continue to feed regularly on rodents, a retention feat that may be the longest in the animal kingdom. By contrast, Dr. Lillywhite said, semiarboreal vipers defecate in a more timely fashion after a meal, usually in a few days, if not hours.

Ground-dwelling vipers store up so much offal, the researchers calculated, that their body mass ends up being as much as 20 percent fecal matter, the vast bulk of it concentrated in the posterior. Unlike cases of pathological constipation that afflict other animals, including humans, the snakes show no ill effects, no vomiting and no signs of septicemia.

Dr. Lillywhite suggests that a land-based viper retains feces because it is a great ballast. It helps anchor the lower body to the ground and thus enables the snake to strike its head out toward prey with great speed and accuracy. Tree-dwellers, by contrast, can use a branch to steady themselves.

Best of all, feces is metabolically inert. Extra muscle, bone or fat require energy to sustain them, while feces sits there for free.

Snakes, as it happens, are sublimely inert themselves, spending less than 5 percent of their lives in motion. For all their fearsome reputation, vipers do not bite unless they really have to.

Three-quarters of the rattlesnake bites in this country are described by herpetologists as ''illegitimate,'' a result, according to Dr. Erika Nowak of the Southwest Biological Science Center of the United States Geological Survey, ''of people who knew what they were doing, who knew that they were dealing with a rattlesnake but just kept poking it or picking it up or bothering it repeatedly.''

Dr. Nowak, whose center is in Flagstaff, Ariz., labors mightily to convince people that having a rattlesnake in the neighborhood is not a menace. Rattlesnakes go to great lengths to avoid biting people or having anything to do with them at all. Even stepping on a rattlesnake is usually a nonevent, and most people have no idea when they have done it, she said.

The site where she conducts her research, the Montezuma Castle National Monument in Arizona, has a ''healthy'' rattlesnake population, 75 to 100 snakes a square mile. About a million people a year visit the monument, she said. Yet in the nine years that she has worked there, two people have been bitten, and one was somebody working for her.

Dr. Nowak strives to improve the rattlesnake's image to limit the number of people who call the authorities and demand that a ''nuisance'' snake in their vicinity be moved elsewhere. Her research has shown that moving snakes far from their homes almost never works. Much of the time, the snakes die as a result. In other cases, they simply return, traveling miles over a period of months or years, until they find their way home, where all they want to be is left alone.

Correction: December 16, 2002

An article in Science Times on Tuesday about the diverse nature of vipers classified coral snakes and black mambas incorrectly. While they are also venomous snakes, they are in the family of elapids rather than vipers.

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A version of this article appears in print on December 10, 2002, on Page F00001 of the National edition with the headline: Venomous and Sublime: The Viper Tells Its Tale. Order Reprints|Today's Paper|Subscribe